help with this newbie question regarding batteries- Mtbr.com

# Thread: help with this newbie question regarding batteries

1. ## help with this newbie question regarding batteries

Hi, I have 12 volt battery system and lights. I've been using \$100 batterspace 9800 mh batteries that are balanced, well built with all the necessary circuits and protections and claim to put out 12.8 volts. They cost \$100 and are highly recommended.

I've noticed a bunch of el cheapo CCTV batteries from China that have similar specs but for only \$40 and without any of the circuits. They say they put out 12 volts but some people say its more like 11.5.

Question- if the Batteryspace battery powers my lights for 3 hours, if I hook up both batteries using a y connector to my lights, is it reasonable to assume that the lights would last AT LEAST 4.5 hours?

Any additionl worries or dangers from doing this as opposed to just running one till it dies and then switching over to the other?

2. Lets start with the basics. AFAIK no battery puts out a constant voltage - they all have a range of voltage and drop from full to empty. Even a 12V car lead acid battery is ~14V when fully charged.

The CCTV cells you are referring to are most likely to be Li-ion.

Li-ion batteries have a nominal voltage of 3.7V ,but actually operate in the range 4.2-3 V, - so 3 li-ion cells in series gives you a range of 12.6 - 9 V. A battery built this way might be variously described as 12.6V (3 x 4.2) or 11.1V (3 x 3.7). The chemistry & number of cells in series dictates the voltage.

Can you provide a link to the battery you are using ?

12.8V says you are not running a li-ion battery & suggests LiFePO4. The different chemistry in the cells means three things (1) lower energy density - ie more weight for the same mAh (2) a lower voltage & (3) a much tighter voltage range.

A LiFePO4 has a nominal voltage of 3.2V but it has a narrower range, 3.6-3.0V. So 4 cells gives a nominal voltage of 12.8V and a range of 14.4-12V

Long story short

If you are using a LiFePO4 battery, I would strongly recommend against using it and a li-ion battery through a y connector - a freshly charged LiFePO4 will try to charge the li-ion battery past its maximum safe voltage of 12.6V.

Nothing good has ever come from this

3. Gotcha. so don't mix em. Here's the link to the li ion battery 12V 9800mAh Super Powerful Rechargeable Protable Li ion Battery with EU Plug | eBay

4. OK, call me a n00b on this as I maybe missing something..........

Why not just carry the CCTV battery and hook it up when your main dies?

5. Yes, that is what I currently do. If its in a rare enduro race or big group ride, I'dlike to not stop.

Thx

jv

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